Fossil evidence suggests that extant North American lizard genera (north of Mexico) evolved during the Miocene. Although fossils of the clade Phrynosomatidae (spiny lizards and sand lizards) have been reported, there have been no previously described fossils of the fringe-toed sand lizards (Uma). In the extant biota, Uma inhabit arid deserts, and members of the western clade of Uma are restricted to sand dunes or other habitats containing fine-grained sand. I describe the first known fossil of Uma and refer the fossil to the total clade of Uma with an apomorphy-based diagnosis. The fossil is a partial premaxilla that was found in the Miocene strata of the Dove Spring Formation of southern California, dating to 8.77 Ma. The paleoenvironment of the Dove Spring Formation was semiarid and contained ephemeral streams that facilitated deposition, and there is no evidence of sand dune deposits in the strata containing the locality from which the Uma fossil was found. Divergence time analyses of a concatenated molecular dataset with four fossil calibrations support a Neogene origin of the total clade of Uma and of the crown clade of Uma. Those analyses also estimated a Neogene divergence between Uma scoparia and the Uma notata complex. Multispecies coalescent analyses with one fossil calibration inferred a Paleogene origin for the total clade of Uma and a Pliocene or Pleistocene divergence between Uma scoparia and the Uma notata complex. The fossil and the total and crown clades of Uma precede the evolution of modern desert ecosystems in the southwestern United States and northern Mexico by millions of years. The total clade and the crown clade of Uma were not restricted to arid deserts throughout their evolutionary histories. I demonstrate that an apomorphy-based diagnosis can be used to identify fossils of isolated skeletal elements for at least one clade of phrynosomatid lizard, and suggest exercising caution when using environmental tolerances of extant taxa to hypothesize paleoecological reconstructions.

中文翻译：

---

第一个已知的乌玛化石：生态进化和北美流趾蜥蜴的起源

化石证据表明，现存的北美蜥蜴属（墨西哥北部）是在中新世时期进化的。尽管有蜥蜴科（刺蜥蜴和沙蜥蜴）化石的报道，但之前没有描述过流趾沙蜥蜴（Uma）的化石。在现存的生物群中，乌玛栖息在干旱的沙漠中，乌玛西部分支的成员仅限于沙丘或其他含有细粒沙的栖息地。我描述了第一块已知的乌玛化石，并通过基于无源性的诊断将该化石归入乌玛的总进化枝。该化石是在南加州 Dove Spring 组中新世地层中发现的部分前颌骨，年代可追溯至 8.77 Ma。多夫泉地层的古环境是半干旱的，并含有促进沉积的短暂溪流，并且没有证据表明乌玛化石发现地所在的地层中存在沙丘沉积。对具有四个化石校准的串联分子数据集的发散时间分析支持 Uma 总进化枝和 Uma 冠进化枝的新近纪起源。这些分析还估计了 Uma scoparia 和 Uma notata 复合体之间的新近纪分歧。通过一种化石校准进行的多物种聚结分析推断出 Uma 整个分支的古近纪起源以及 Uma scoparia 和 Uma notata 复合体之间的上新世或更新世分歧。乌玛的化石以及总进化枝和冠进化枝比美国西南部和墨西哥北部现代沙漠生态系统的进化早了数百万年。乌玛的总进化枝和冠进化枝在整个进化史上并不局限于干旱沙漠。我证明基于无源性的诊断可用于识别至少一个蜥蜴分支的孤立骨骼元素化石，并建议在使用现有类群的环境耐受性来假设古生态重建时要小心谨慎。